1. Field of the Invention
The present invention relates to a scanning optical system such as a printer which forms an image by an electrophotographic process.
2. Related Background Art
FIG. 1 shows an overall configuration of a prior art laser beam printer which is an image recorder by an electrophotographic process. Numeral 100 denotes a printer body, numeral 102 denotes a cassette for accommodating transfer sheets S, numeral 104 denotes a feed roller for taking the transfer sheets S one by one from the cassette 102, numeral 105 denotes a separation pad for separating each of the sheets S, numeral 106 denotes a regist roller for controlling a feed timing of the transfer sheets S, numeral 108 denotes a transfer charger, and numeral 110 denotes a process cartridge which contains therein a photoconductor drum 112, a developing unit (not shown), a charger (not shown), and a cleaning unit (not shown) for the drum 112. Numeral 114 denotes a fixing unit, numeral 116 denotes a fixing roller made of an aluminum pipe, numeral 117 denotes a halogen heater, and numeral 118 denotes a rubber pressure roller. Developing agent on the transfer sheet S is solved and fixed by heat and pressure applied-by the fixing roller 116 and the pressure roller 118. Numeral 120 denotes a convey roller, numeral 122 denotes an ejection roller, numerals 124a and 124b denote decurling rolls and numeral 126 denotes an ejection tray.
A laser scanner unit 101 for scanning a laser beam L is provided in the printer body 100. The laser beam L is reflected by a mirror 103 and directed to the photoconductor drum 112.
When a print signal is applied to the printer from a host computer (not shown), the transfer sheet S is taken out of the cassette 102 by the feed roller 104 and fed by the regist roller in a timed fashion with a developing image on the photoconductor drum 112. An image written on the drum 112 by the laser beam L is transferred to the transfer sheet S. Then, the transferred image is fixed by the fixing unit 114 and the transfer sheet S is fed and ejected by the convey roller 120 and the ejection roller 122, and stacked on the ejection tray 126.
FIG. 2 shows a plan view of a laser optical system in the laser scanner unit 101. A light beam emitted from a laser oscillator 107 is reflected by a mirror surface of a polygon mirror 111 supported by a polygon rotor 109 which is rotated at a constant velocity in a direction a so that it is scanned in a main scan direction (arrow b). The light beam thus scanned passes through a focusing lens 113, is reflected by a reflection mirror 103 and directed to and focused on the drum 112. Since the drum 112 is rotated in a sub-scan direction (which is perpendicular to the main scan direction and an optical axis of the optical system) by a predetermined amount for each scan, a two-dimensional image is formed on the drum 112 by the scanned light beam L.
On the other hand, the scanned light beam at the start of the scan is reflected by a reflection mirror 115 in each scan, and the reflected light is directed to a DC controller by an optical fiber 119 as a horizontal synchronous signal (which is a signal for determining a start position of recording in order to maintain a constant start position of scanning on the drum, and which is hereinafter referred to as BD). The rotation of the polygon mirror is controlled by a motor driver circuit card 123 which is accommodated in a housing 125.
The above prior art system includes the following shortcoming.
As shown in FIG. 2, the focusing lens 113 and the scanner motor including the polygon mirror 111 are mounted on the housing 125 of the laser scanning optical system. Accordingly, the housing 125 of a precise and complex shape to accommodate those parts is required. This increases cost.
Further, since the BD circuit in the DC controller 121 is located externally of the housing 125 of the laser scanning optical system, connection means such as optical fiber 119 is required.